17/10/2016 | Why world leaders are meeting to discuss hydrofluorocarbons

The Economist Staff

IN 1985 a gaping hole was found in the ozone layer above Antarctica. Two years later leaders from around the world signed the Montreal Protocol, a treaty to phase out the substances causing it, known as chlorofluorocarbons (CFCs), which were used in refrigeration and as propellants in products such as hairsprays and deodorants.

Scientists had discovered more than a decade earlier that CFCs release chlorine into the stratosphere as they decompose—depleting ozone—and are also powerful greenhouse gases. Thanks to the treaty, the equivalent of some 135 billion tonnes of carbon-dioxide emissions were avoided, saving the ozone layer from complete collapse by the middle of this century. This week officials from around the world, led by America and China, are meeting in Rwanda to make a deal that would extend the Montreal Protocol to cover hydrofluorocarbons (HFCs), which were introduced to replace CFCs. Why?

HFCs don’t deplete the ozone layer but they still contribute hugely to global warming, as scientists discovered in the decades after their introduction. The average atmospheric lifetime for most commercially used HFCs is 15 years or less whereas carbon dioxide can stay in the atmosphere for more than five centuries. But, like CFCs, HFCs cause a greenhouse effect between hundreds and thousands of times as powerful as carbon dioxide. Total emissions of HFCs are still relatively low. But they are rising by 7-15% a year as people in hot countries, such as Brazil and India, become richer and buy air-conditioning units.

Small island nations, which are most susceptible to the effects of climate change, have been discussing the need to control HFC emissions for a decade. China and America promised to do something about them in 2013. America wants action to be speedy enough for global emissions to reach their peak by 2021, then to start falling; China may be keener to postpone that point until 2023. Brazil, Indonesia and Malaysia lean towards 2025. India has lobbied for an even later date, closer to 2030. But many African countries and low-lying island states, already concerned by global warming, are pushing for a tighter timetable. Whatever the deadline, and however steep the cuts, the plan is to require rich countries to act faster while allowing poorer ones more time to adjust.

A deal on HFCs would quickly benefit the climate—and not just by obliging countries to cut emissions of these powerful greenhouse gases. On its own this direct effect could make a real difference. An ambitious deal, for example one demanding that they start to be phased out by 2020, would cut the equivalent of between 100 billion and 200 billion tonnes of carbon-dioxide emissions by 2050, enough to chop 0.5°C from the rise in average global temperatures by 2100. But, as the history of CFCs suggests, extending the Montreal Protocol to include HFCs could also benefit the climate by boosting the efficiency of air-conditioning units. After the original deal some coolers were 60% more efficient than the ones they replaced. Similar adjustments to an expanded agreement could make such technologies more environmentally friendly overall. This is particularly important because they happen to be both a cause of global warming, and an important means of adapting to it.